Hydraulic torque wrenches are well known power tools for tightening and loosening nuts and bolts. A hydraulic pump commonly pressurizes a hydraulic fluid that is circulated to and from the hydraulic torque wrench via hoses. The hydraulic torque wrench itself commonly features a piston that transforms the fluid pressure into a piston force, which in turn is transferred via a piston rod onto drive plates, and via one or two pawls onto a ratchet wheel that is sandwiched between the drive plates. The ratchet wheel commonly connects to a nut or itself has an internal cutout that matches the nut or bolt head to be tightened or loosened.
Since nuts and bolts are commonly tightly assembled, it is desirable to have a hydraulic torque wrench as compact as possible while at the same time providing a maximum torque and reliable and lasting functionality. The weakest link in the force transmission path from the hydraulic piston to the ratchet wheel is/are commonly the pawl(s) that has/have to reliably engage with a corresponding tooth of the ratchet wheel. Ratchet wheel and pawl(s) are assembled in a cartridge between two lateral plates as is well known in the art. During return travel of the hydraulic piston, the pawl(s) has/have to disengage with the ratchet wheel. Since the pawl(s) is/are much closer positioned to the torque transfer axis than the commonly more peripheral piston rod—drive plate interface, the actual force transmitted across the pawl(s) is in accordance with the well known lever principle substantially higher than the actually produced piston force. Excessive wear commonly occurs in the plate-pawl and pawl-tooth interfaces. Therefore, there exists a need for improved plate-pawl and pawl-tooth interfaces. The present invention addresses this need.
Two cartridge pawls have been employed in the prior art to divide the force to be transmitted onto the ratchet wheel. Nevertheless, it has been discovered by the Applicant that deformation during power strokes causes displacement of the pawls resulting in uneven loads and contact pressures. The present invention addresses this discovery for balanced load and contact pressures in all plate-pawl and pawl-tooth interfaces providing for up to three cartridge pawls to be employed simultaneously.
Ratchet cartridges need to be conveniently replaced especially in cases where the ratchet wheel itself connects to the nut and/or bolt head to be tightened and loosened. Nevertheless, in the prior art commonly the piston rod had to be taken apart in order to remove the ratchet cartridge from the overall torque wrench housing. Therefore, there exists a need for a simple and reliable connection between ratchet cartridge and piston rod that can be fast and easily disconnected and reconnected. The present invention addresses also this need.